Bone Tissue and the Skeletal System

Overview of the Skeletal System

The human skeletal system is composed of 206 bones in adults and serves as the framework for the body. It is made up of osseous tissue (bone tissue), cartilage, and ligaments. Each component plays a vital role in the structure and function of the skeleton.

• Osseous tissue: The primary tissue forming bones, providing strength and support.

• Cartilage: Forms most embryonic bones, covers many joint surfaces in the mature skeleton, and is surrounded by the perichondrium (a dense connective tissue layer that resists outward expansion).

• Ligaments: Connect bones together at joints, contributing to stability.

Functions of the Skeletal System:

• Support: Provides a structural framework for the body.

• Protection: Shields vital organs (e.g., skull protects the brain).

• Movement: Acts as levers for muscles to produce movement.

• Electrolyte balance: Stores minerals such as calcium (Ca) and phosphorus (P), essential for various physiological processes.

• Triglyceride (fat) storage: Stores energy in the form of fat within yellow bone marrow.

• Acid-base balance: Buffers blood against pH changes using alkaline salts.

Cartilage: Structure, Types, and Locations

Types of Cartilage

Cartilage is a flexible connective tissue found in various parts of the body. It is classified into three main types based on fiber composition and function:

• Hyaline cartilage: Most abundant type; provides support, flexibility, and resilience. Contains only collagen fibers. Found in articular surfaces of joints, costal cartilage (ribs), respiratory structures (larynx), and nasal cartilage (nose tip).

• Elastic cartilage: Similar to hyaline cartilage but contains elastic fibers, allowing for greater flexibility. Located in the external ear and epiglottis.

• Fibrocartilage: Contains thick collagen fibers, providing great tensile strength. Found in the menisci of the knee and intervertebral discs.

Perichondrium: A dense connective tissue layer that surrounds cartilage, providing nutrients and resisting outward expansion.

Growth of Cartilage

Cartilage grows by two mechanisms:

• Appositional growth: Cartilage-forming cells in the perichondrium secrete new matrix on the external surface of existing cartilage.

• Interstitial growth: Chondrocytes within lacunae divide and secrete new matrix, expanding cartilage from within.

Classification of Bones

Bone Types and Functions

Bones are classified by their shapes, which relate to their functions in the body. The main types are:

• Long bones: Act as levers for movement (e.g., humerus, femur).

• Short bones: Provide stability and support with limited motion (e.g., carpals, tarsals).

• Flat bones: Serve as points of muscle attachment and protect internal organs (e.g., sternum, ribs, scapulae, cranial bones).

• Irregular bones: Have complex shapes for specialized functions (e.g., vertebrae, facial bones).

• Sesamoid bones: Small, round bones embedded in tendons, protecting them from compressive forces (e.g., patella).

Bone Classification Table

The following table summarizes the main bone classifications, their features, functions, and examples:

Example: The femur is a long bone that acts as a lever to facilitate movement, while the patella is a sesamoid bone that protects the knee joint.

Additional info: Bone classification is essential for understanding skeletal function, injury patterns, and clinical approaches in orthopedics and anatomy.